1. Field of the Invention
Thermal power measurement.
2. Description of the Prior Art
A need exists for obtaining an absolute measurement of the thermal power generation or consumption of any system using flowing fluid for heat transport. For example, in a nuclear reactor power plant, a typical arrangement includes a nuclear reactor and a steam generator with circulating fluid being provided from the reactor to the generator by way of an outlet leg (hot leg) with fluid being returned back to the reactor from the generator by way of an inlet leg (cold leg) in a closed loop known as the primary loop. The steam generator in turn may be connected to a power generation device such as a turbine in another closed loop known as the secondary loop.
In the nuclear plant, the thermal power of the primary loop is the power which the nuclear reactor is producing and is measured in thermal energy per unit of time. The thermal power of the secondary loop is the power that the steam generator provides and should be equal to the thermal power of the primary loop. Nuclear regulations require that the plant be operated at certain prescribed ratings and knowledge of thermal power would insure conformance with the requirement. In addition, measurements are needed to account for fuel burnup and to calibrate power control systems. Of equal importance is the fact that thermal power measurement provides an indication of the plant efficiency.
In addition to nuclear plants, thermal power knowledge is also desirable in fossil fuel power plants as well as other closed loop systems such as heat exchangers and chemical reactors. There is however, no available system which will provide a thermal power measurement to a high degree of accuracy, such as one percent or less. For thermal power measurement the flow rate of the circulating fluid must be known as well as other of its properties, such as density and enthalpy, which is a quantity established by arbitrary definition and is the sum of the internal energy and potential energy of the fluid. Other terms such as total heat, heat content, and thermal potential have been used; however, the designation enthalpy is preferred.
In presently proposed systems, measurement of fluid pressure and temperature are required. The pressure of the circulating fluid in such systems typically may be in the order of thousands of psi and the variation of pressure during operation is relatively small and insignificant. Accordingly, no difficulty is encountered in the obtaining of pressure measurements. With respect to temperature measurements, however, wherein the circulating fluid is a liquid, temperature gradients exist across the fluid in the duct and a single temperature measurement such as obtained by a thermocouple near the fluid-duct interface, may not accurately represent the average temperature of the fluid in the duct passing that thermocouple. Multiple thermocouples may be positioned around the duct, however, the same problem exists. To provide a fair indication of the temperature across the fluid a plurality of thermocouples would have to be positioned at various points within the duct; however this is objectional since it presents an obstruction to fluid flow, and if a thermocouple or thermal measuring device should break loose, it could cause significant damage.